The first cause of a weak essay is not a shortage of ideas. It is too much subject.

"The future of education" is not a topic; it is a library. "What role should technical training play in the development of inland provinces?" is a question ten pages can answer.

Narrowing happens along three axes: the object (what exactly is under discussion), the place (where) and the period (when). Every axis left open multiplies what you would have to establish, and an essay that must establish everything establishes nothing.

A narrow question well answered is always worth more than a broad one skimmed. It is also, in practice, far easier to write, which is the part students discover last.